Gynecomastia, defined as the enlargement of male breast tissue in men, is a relatively common finding, frequently observed in newborns, adolescents, and old men. Physiological gynecomastia, occurring in almost 25% of cases, is benign and self-limited; on the other hand, several conditions and drugs may induce proliferation of male breast tissue. Gynecomastia is often related to estrogen excess and/or androgen deficiency as a consequence of different endocrine disorders. Non-endocrine illnesses, including liver failure and chronic kidney disease, are other causes of gynecomastia that should be considered. Due to the diversity of possible etiologies, including neoplasm, performing a careful history and physical examination is mandatory. Once gynecomastia has been diagnosed, treatment of the underlying cause is warranted. If no underlying cause is discovered, then close observation is appropriate. If gynecomastia is severe and/or painful, however, medical therapy can be attempted, and if ineffective, glandular tissue can be removed surgically.